Hydrofluorocarbons (HFC) and in particular hydro-fluoroolefins, such as 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) are compounds known for their properties of refrigerants and heat-exchange fluids, extinguishers, propellants, foaming agents, blowing agents, gaseous dielectrics, monomer or polymerization medium, support fluids, agents for abrasives, drying agents and fluids for energy production units. Unlike CFCs and HCFCs, which are potentially dangerous to the ozone layer, HFOs do not comprise chlorine and thus do not present a problem for the ozone layer.
Several processes for the manufacture of HFO-1234yf are known.
WO 2009/084703 describes a process for the manufacture of HFO-1234yf from hexafluoropropene involving the intermediacy of hexafluoropropane, pentafluoropropene, and pentafluoropropane.
WO 2007/079431 describes the preparation of HFO-1234yf by a process comprising the stages of fluorination of 2-chloro-3,3,3-trifluoro-1-propene (HCFO-1233xf) to give 1,1,1,2-tetrafluoro-2-chloropropane (HFC-244bb), followed by a dehydrochlorination stage. The product HCFO-1233xf is prepared by fluorination of the corresponding chlorinated precursor (CCl2═CClCH2Cl).
WO 2008/054781 describes a preparation of HFO-1234yf by reaction of 2,3-dichloro-1,1,1-trifluoropropane (HFC-243db) in the presence of HF over a catalyst, in particular 98/2 Cr/Co. The reaction products comprise HFO-1234yf and 2-chloro-3,3,3-trifluoro-1-propene (HCFO-1233xf), the latter product being predominant; the other products 1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zd) and also 1,1,1,2,2-pentafluoropropane (HFC-245cb) and 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze) are also formed. A higher temperature favors the production of the 1233zd isomer. The starting material, 2,3-dichloro-1,1,1-trifluoropropane (HFC-243db), is indicated as being obtained by chlorination of trifluoro-1-propene (TFP).
WO 2008/040969 and WO 2008/075017 describe a substantially similar preparation. It is indicated that the reaction proceeds by dehydrochlorination of HFC-243db to give HCFO-1233 (both xf and zd), followed by a reaction involving the formation of 1,1,1,2-tetrafluoro-2-chloropropane and the formation subsequently of the desired 2,3,3,3-tetrafluoro-1-propene by dehydrochlorination. The HF:organics ratio is varied and it is indicated that the dehydrochlorination reaction to give HCFO-1233 (xf and zd) is favored by low HF:organics ratios while the reaction for the preparation of the desired final compound is favored by high HF:organics ratios. The starting material, 2,3-di-chloro-1,1,1-trifluoropropane (HFC-243db), is indicated as being obtained by chlorination of trifluoropropene or trifluoromethylpropene.
WO 2010/123154 describes a preparation of HFO-1234yf by reaction of HCFO-1233xf with HF in the presence of oxygen and of a catalyst comprising chromium oxide CrOm with 1.5<m<3. This document teaches the use of an oxygen/HCFO-1233xf molar ratio at most equal to 1 in order to improve the selectivity.
Furthermore, the document US 2011/245548 describes the use of a molar ratio of oxygen with respect to a chlorinated compound of between 0.1 and 1 in order to increase the lifetime of a catalyst in the fluorination reaction of pentachloropropane or tetrachloropropene to give HCFO-1233xf.
The preparation methods as mentioned above generally comprise several stages and require very expensive capital costs. In addition, it is often complex to implement them on an industrial scale. The presence of byproducts which cannot be recovered in value and also the lifetime of the catalyst are among the most frequently encountered problems when moving on to the industrial scale.
Furthermore, the presence of oxygen in an amount as described in the prior art presents numerous problems: formation of oxygen-comprising byproducts; formation of water, which, in the presence of HF, results in a highly corrosive medium and safety (risk of ignitibility of the gaseous effluent) in the reactor or downstream of the reactor in the separation units.
There exists a need for a process for the preparation of HFO-1234yf from a starting material which is readily accessible and easy to employ, resulting “on a long-term basis” in the desired product with a high selectivity and advantageously a high yield and/or conversion.